1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, particularly to an improved intermediate layer which makes it possible to provide an electrophotographic photosensitive member excellent in production stability, image quality and durability of electrophotographic photosensitive member.
2. Related Background Art
Since discovery of specific organic compounds which exhibit photoconductivity, a large number of organic photoconductive materials have been developed. For example, organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, et., low molecular weight organic photoconductive materials such as carbazole, anthracene, pyrazolines, oxathiazoles, hydrazones, polyarylalkanes, etc., or organic pigments or dyes such as phthalocyanine pigments, azo pigments, cyanine dyes, polycyclic quinone pigments, perylene type pigments, indigo dyes, thioindigo dyes or squaric acid methine dyes, etc., have been known. Particularly, organic pigments or dyes having photoconductivity can be synthesized more easily as compared with inorganic materials, and yet variation for selecting compounds exhibiting photoconductivity at an appropriate wavelength region is enlarged, and therefore, a large number of photoconductive organic pigments and dyes have been proposed. For example, as disclosed in U.S. Pat. Nos. 4,123,270, 4,247,614, 4,251,613, 4,251,614, 4,256,821, 4,260,672, 4,268,596, 4,278,747 and 4,293,628, electrophotographic photosensitive members are known using disazo pigments exhibiting photoconductivity are the charge generation substance in the photosensitive layer having the functions separated into the charge generation layer and the charge transport layer.
Since such an electrophotographic photosensitive member using an organic photoconductive material can be produced by coating with selection of an appropriate binder, productivity is extremely high to provide an inexpensive photosensitive member, and yet the photosentive wavelength region can be advantageously controlled freely by selection of the organic pigment.
Among them,, the lamination type photosensitive member obtained by lamination of a charge transport layer and a charge generation layer composed mainly of la charge generation material is more excellent in residual potential, memory, repeating characteristics, etc., as compared with other single layer type photosensitive members, particularly having advantage in improvement of sensitivity. However, in recent years, it has been desired to develop an organic photosensitive member having sensitivity, memory, repeating characteristic, durability which is equal to or getter than inorganic photosensitive member of high sensitivity such as a-Se type, CdS type, a-Si type, etc. However, under the present situation, there are a large number of unresolved problems for development of organic photosensitive members having such high performances.
Particularly, organic photosensitive members are weak in mechanical strength and, when applied to copying machines, printers, etc., pinholes, fine cracks, friction at end portions, peel-off, etc., occur in the photosensitive member to cause formation of image defects.
Also, organic photosensitive members are generally coated as thin films with 10 to 40 .mu.m thickness on the electroconductive support, and therefore disturbance of coated films is liable to occur through the defects such as impurities, damages, striken marks, foams, etc., on the supports, thereby causing image defects.
Particularly in the case of the so called function separation type organic photosensitive member comprising a charge transport layer (CTL) laminated on a charge generation layer (CGL), it is extremely highly sensitive as compared with the former with little residual potential, while it has the drawbacks of large dark decay, and optical memory. As a countermeasure against these problems, it is required to make the charge generation layer further thinner (generally 0.01 .mu.m to 6 .mu.m). Accordingly, the photosensitive member is further susceptible to the influences by the defects on the support such as projections, sinks, damages, striken marks, etc., whereby various image defects are caused and no image of high quality can be obtained under the present situation.
For solving such problems, it has been attempted in recent years to provide an electroconductive layer composed mainly of an organic polymer between the support and the charge generation layer. According to this technique, image defects and lowering in image quality due to the repeating use can be reduced.
Since the electroconductive layer is generally made to have a film thickness of 10 to 50 .mu.m, it is required to have a considerably low electrical resistance. Generally speaking, it is demanded to have a specific resistance value of 10.sup.14 .OMEGA.. cm or less, preferably 10.sup.12 .OMEGA.. cm or less, and for accomplishing the target, it has been also known to formulate organic or inorganic electroconductive substance, ionic substances, etc., in the organic polymer. Such an electroconductive layer is subject to injectability of charges, and injection of charges can be impeded by providing an adhesive layer between the electroconductive layer and the charge generation layer.
As the material to be used for the adhesive layer, organic polymers are used. However, since they have generally great electrical resistance to cause lowering in sensitivity and increase of residual potential, a thin film with a thickness of 5 .mu.m or less, particularly 0.1 to 2 .mu.m has been practically used.
Accordingly, the surface characteristic of the intermediate layer, particularly the surface characteristic of electroconductive layer or the surface characteristic of the adhesive layer gives great influences to the image characteristics and durability characteristics. Particularly, when no sufficient adhesive strength can be obtained between the electroconductive layer and the adhesive layer, or between the adhesive layer and the photosensitive layer, or between the electroconductive layer and the photosensitive layer, when the photosensitive member is subjected to prolonged use, pinholes, cracks, peeling, fractures, etc., from the end portions of the photosensitive layer may occur to cause remarkable lowering in image characteristics and durability characteristics.
Also, by use of a thermosetting resin as the organic polymer in the electroconductive layer, particularly resistance to friction, peeling, etc., at the end portion of the photosensitive member should be further improved, but when it is made as a smooth surface, rather adhesive strength with the adhesive layer is lowered as compared with the case of the thermoplastic resin.
Also, in recent years, development of printers, etc., a printer utilizing laser beam (LBP), LED, and a printer utilizing liquid crystal shutter, etc., have been popularly practiced, but particularly in the case of LBP, phenomenon which is called interference of laser beam occurs to form the so called interference fringe on the image.
For prevention of such interference fringe, various techniques have been investigated, and as one of the most effective techniques, there has been already known the method to roughen the surface of the support.
As the method for roughening the surface of the support, there have been known the chemical method (e.g. etching), the mechanical method (e.g. sand blast, grinding by bite), etc., but each method not only involves difficulty in pollution problem, production stability, and production cost, but also there is great variance in surface roughness and a difficulty in control of characteristic.
When the surface has become irregularly rough, injection of charges, pinholes, etc., may partially occur to cause image defects such as black dot, white dot, fog, etc., and therefore this method is still in unsatisfactory stage in practical application.
On the other hand, it has been also known to utilize an electroconductive layer. For example, it has been known to roughen the surface according to such methods as addition of coarse irregularly shaped particles into the electroconductive layer, addition of irregularly shaped fine particles with great agglomerating tendency, generation of orange peel or cell structure (Benard convection cell) on the coating by combination of solvents, formation of nonuniform interface by addition of different kinds of resins, etc.
Among them, addition of coarse irregularly shaped particles or irregularly shaped fine particles with great agglomerating tendency is an effective tehnique with relatively eacy control of the surface roughness, but also irregular coarse defects are formed on the surface, whereby great problems such as black dots, fog, etc., occur on the image under the present situation. Practically speaking, addition of coarse irregularly shaped particles with mean particle sizes or 1 to 2 .mu.m or more can effectively roughen the surface of the electroconductive layer, but such particles are generally liable to be sedimented, and it is difficult to maintain uniform state in a coating solution formulated by the dispersion, whereby it is difficult to carry out stable production (to obtain stable surface roughness) under the present situation.
On the other hand, with irregularly shaped fine particles with a mean particle size of 0.5 .mu.m or less, they have generally no effect of roughening the surface when dispersed uniformly in a binder solution. However, in the case of irregularly shaped particles with great agglomerating tendency, also in the case of relatively poor affinity between the particles and the binder, the coated surface can be roughened by agglomeration of the fine particles. However, in this case, it is very difficult to control the degree of agglomeration, whereby not only great defects are irregularly formed on the surface, but also agglomeration of fine particles occurs in the coating solution and it is extremely difficult to obtain production stability as a great obstacle in practical application under the present situation.